This invention relates to a fuel system shut-off valve.
It is conventional to use a so-called common rail storage injection system in connection with an internal combustion engine. In such a system, fuel under injection pressure is injected into a combustion chamber of the engine by controlling an injection valve. If the injection valve is defective, this enables the situation in which fuel may leak in uncontrolled fashion into the combustion chamber. To prevent this, the publications U.S. Pat. No. 3,780,716 and WO 95/17594 propose a shut-off valve for limiting the fuel flow volume. The shut-off valve has a cylinder space which contains a piston provided with a spring load acting against the fuel flow direction in an injection situation. In normal operation the fuel amount needed for each injection corresponds to the volume displaced by the piston movement. If for some reason the shut-off valve continues to leak, the piston moves to an extreme position in which it shuts the flow off.
In publication GB 2317922 there has been disclosed another shut-off valve for limiting the flow volume. In the initial situation, the pressure acts upon a smaller surface area on the fuel admission side in which case, at a given pressure, the force is naturally smaller being in proportion to the surface area acted upon. However, a disadvantage of this solution is the absolute tightness requirement and consequently it is very sensitive in regard to the fuel quality. If the sealing surface of this smaller surface area leaks, the solution does not work and the pressure is applied to the entire surface area and the piston may move to an extreme position in which it closes the flow. Especially in a large power plant or marine engine the fuel can be such that the solution does not function reliably enough.
Also, the prior art flow shut-off valves have generally problems related to situations in which the fuel viscosity is high, for example when heavy fuel oil is used and/or when the fuel temperature before starting the engine is lower than the normal operating temperature. Consequently, the equalization of the fuel pressure over the piston does not occur rapidly enough and the piston may move to an extreme position and close the injection connection.
An object of the present invention is therefore to provide a fuel system shut-off valve by which the prior art disadvantages are avoided. An objective of the present invention is especially to provide a shut-off valve by which the unintentional closure on starting phase can be avoided.